Passenger safety systems heretofore found in vehicles such as automobiles and aircraft have been of two principal types, specifically, seat belts and airbags. Possibly the earliest to be used was the passenger lap belt which was attached to fixed sub-structure at each end and was joined over the users lap by suitable buckling devices. Normally one of the two pieces making up the belt was of fixed length while the length of the other piece could be adjusted in order that the belt could accommodate users of all sizes. This type of belt was used for many years in automobiles and remains to this day the principal type of safety restraint used for passenger restraint in private and commercial aircraft.
At a later time, to further protect against possible injury, the lap-belts in automobiles were modified to include a shoulder strap that was attached at a third fixed point to restrain the passenger's upper torso against forward movement in a crash event. The latest significant protective equipment added was, in the case of passenger automobiles, the provision of passive restraints, or airbags. These bags, which are inflated by compressed air or other gases, are mounted in the automobile steering column and in other fixed locations within the automobile, such as the dash board and side panels. In the event of sudden deceleration of the auto, as in a crash, sensors identify the event and the compressed air or other gases are released to expand the bags at high speeds directly toward the passengers to prevent their forward movement. Airbags have proven generally effective in providing passenger protection, especially when used in conjunction with safety belt restraints.
While airbags are now common as passive restraints for front seat passengers in automobiles their use is not equally widespread in trucks and related commercial vehicles nor are they used in automobile rear seat locations. Further, the use of seat mounted airbags for passenger protection in aircraft has not occurred, for reasons having to do primarily with aircraft design and use, seat design and seat location. Seats in commercial passenger aircraft, unlike those in land vehicles, are not fixed in a permanent position but rather are movable to different locations so that, as one example, more or less space can be provided between succeeding rows and, occasionally, the seats are removed to permit an aircraft to transport cargo rather than people. In addition, the backs of aircraft seats are not rigidly mounted but, rather, they swing forward and down in a crash event, so they cannot be used to store airbags that might be protective in a crash event.